The hazards posed by microorganisms and macroorganisms in the working environment were reviewed. Occupations generally considered to be at risk for this type of occupational hazard included agricultural, medical, and laboratory workers. Agricultural workers at risk included those breeding animals, those cultivating plants, and gardeners. Also at risk were fishermen, forestry workers, orchardmen, veterinarians, animal products workers, leather workers, those employed at plant product processing facilities, textile workers, papermill workers, sawmill operators, health care workers, pharmaceutical workers, beauticians, research workers, miners, printers, those who renovate old articles, sewage and compost workers, solderers, and teachers in day care centers. The biohazards may operate as infectious, allergenic, toxic, or carcinogenic agents in humans. The most important hazardous biological agents included viruses, bacteria, fungi, other plants both lower and higher than fungi, invertebrate animals including arthropods, and vertebrate animals. Recommendations offered include the defining of the most important allergenic and toxic agents occurring in organic dusts and their modes of action on humans, establishing methods for inactivation of hazardous biological agents, developing protective techniques for workers, eradicating water snails, researching pathogenetic properties of wood dust, extending safety precautions, identifying agents causing infections in waste handling workers, and determining the real hazard connected with exposure of workers in the metallurgical industry to oil mist containing microorganisms and their toxins.